Coastal Environments Flashcards
Constructive waves
- long wavelength
- strong swash
- weak backwash
Destructive waves
- tall waves with short wavelength
- weak swash
- strong backwash
What is fetch
Length of time and distance over open water that the wind has blown to create a wave
Examples of erosion
- hydraulic action
- abrasion
- corrosion
- attrition
- etc etc
What is hydraulic action
Waves hit cliffs and force air into cracks
What is abrasion
Waves pick up pebbles and hurl them against the cliff
What is solution (corrosion)
The dissolving of CaCO3 rocks (eg limestone or chalk) by the sea
What is attrition
Pebbles carried by the waves collide with each other and become smaller and more rounded over time
What is deposition
Occurs when waves lose energy material carried is too large to transport with the amount of energy the wave has
What is the process of longshore drift?
- wave swash approaches the beach at a 45-degree angle (the same as the prevailing wind direction)
- this is in conditions where wave refraction is not complete
- backwash is at a 90-degree angle, due to gravity
- process repeats, moving sediment along the beach
- smaller material is transported further as it requires less energy
How are materials moved in water?
- traction
- saltation
- suspension
- solution
What is traction?
When large heavy material is dragged along the sea floor
What is saltation?
When smaller material bounces along the sea floor
What is suspension?
The fine material held in water, ‘suspended’
What is solution
The dissolved material carried in the water
What is the meaning of weathering
When rocks break down in situ
What are the types of weathering?
- mechanical
- chemical
- biological
What are processes of physical weathering?
- freeze-thaw
- salt crystal growth
- wetting and drying of clay rich rocks
How does freeze-thaw work?
- Water gets into cracks and joints in the rock
- When the water freezes it expands and the cracks open a little wider
- Over time, pieces of rock split off the rock face, whilst big boulders are broken into smaller rocks and gravel
How does salt weathering work?
- Water in cracks evaporates leaving salt crystals
- The salt crystals expand and the cracks become larger
- Over time, pieces of rock split off the rock face, whilst big boulders are broken into smaller rocks and gravel
What are the processes of chemical weathering?
- carbonation
- oxidation
- acid rain
- usually impacts CaCO3 rocks
How does chemical weathering generally work?
- Rainwater is slightly acidic through absorbing carbon dioxide from the atmosphere
- This reacts with minerals in the rock, creating new material
- Rock type affects the rate of weathering eg limestones chemically weathers faster than granite
- The warmer the temperature, the faster the chemical reaction
What are the processes of biological weathering?
- plant roots
- burrowing animals
- nesting birds
How does roots of plants break down rock?
- Trees and plants grow in the crack of the rock formation
- As the roots grow bigger, they push open crack sin the rocks, making them wider and deeper
- Over time, the growing tree eventually forces the rock apart
How does microorganisms weather rock?
- Organisms like bacteria, algae and moss can grow on rocks
- These produce chemicals that break down the surface layer of the rock
How does burrowing animals weather down rocks?
- Burrowing animals eg rabbits disturb the ground
- This destabilizes the rock above the burrow
- Increasing pressure on any cracks
- Eventually pieces fall off the rock
What is mass movement?
The downhill movement of material under the influence of gravity
Types of mass movement…
- slumping
- sliding
What is slumping?
When the waves erode the cliff base and cause instability. Rainwater permeates thought eh rock, saturating it, until it becomes unstable and slumps along bedding planes. This leads to a stair-like appearance
What is
When the waves erode the cliff base and cause instability. Rainwater permeates thought eh rock, saturating it, until it becomes unstable and slumps along bedding planes. This leads to a stair-like appearance
What is sliding
When weathering loosens rock, which slides down off bedding planes. Leads to landslides and mudslides. Blocks of rock slides downhill
What is geology
The study of rock type
What is lithology
The study of characteristics of rock eg relative hardness, permeability etc
What is discordant geology / coastline?
Rock outcrops are at 90 degrees to the sea, in alternating layers of hard and soft rock. This leads to headlands and bays.
What is concordant geology/coastline?
Rock outcrops are parallel to the sea, ie only one type of rock along one coastline. Crates coves, eg Lulworth cove, Dorset
What are bedding planes?
The change in sediment texture, structure and or composition, ie differnt type of rock in layers.
How does vegetation influence the coast?
- biological weathering
- can create sand dunes via encouraging deposition, and then stabilizing them
- can protect and preserve coastal landforms by buffering and reducing wave energy (e.g. mangroves)
How does sea level influence the coast?
- flooding, a huge issue associated with rising sea level, especially considering many urban areas are situated on the coast
- saltwater incursion
- creation of landforms (different dependent on whether sea levels are rising or falling - remember this is different in different parts of the world)
What is isostatic readjustment?
When land level rises or falls relative to the sea, so it appears that sea level is falling or rising.
- this leads to relict (old) landforms
- emergent landforms (falling sea level) = raised beaches and cliffs
- submerging landforms (rising sea level) = rias (drowned river valleys) and fjords (drowned glaciated valleys.
